scholarly journals Fast and spectrally accurate evaluation of gyroaverages in non-periodic gyrokinetic-Poisson simulations

2017 ◽  
Vol 83 (4) ◽  
Author(s):  
J. Guadagni ◽  
A. J. Cerfon
Keyword(s):  
Time Complexity ◽  
Numerical Scheme ◽  
Fourier Transforms ◽  
Hankel Transform ◽  
Log P ◽  
Fourier Space ◽  
Compactly Supported ◽  
Geometric Convergence ◽  
Spatial Grid ◽  
Grid Points

We present a fast and spectrally accurate numerical scheme for the evaluation of the gyroaveraged electrostatic potential in non-periodic gyrokinetic-Poisson simulations. Our method relies on a reformulation of the gyrokinetic-Poisson system in which the gyroaverage in Poisson’s equation is computed for the compactly supported charge density instead of the non-periodic, non-compactly supported potential itself. We calculate this gyroaverage with a combination of two Fourier transforms and a Hankel transform, which has the near optimal run-time complexity$O(N_{\unicode[STIX]{x1D70C}}(P+\hat{P})\log (P+\hat{P}))$, where$P$is the number of spatial grid points,$\hat{P}$the number of grid points in Fourier space and$N_{\unicode[STIX]{x1D70C}}$the number of grid points in velocity space. We present numerical examples illustrating the performance of our code and demonstrating geometric convergence of the error.

The extended Fourier algorithm: Application in discrete optics and electron holography

1994 ◽  
Vol 52 ◽  
pp. 918-919
Author(s):  
E. Voelkl ◽  
L. F. Allard
Keyword(s):  
Fourier Transform ◽  
Fourier Transforms ◽  
Sampling Rate ◽  
Electron Holography ◽  
Optical Bench ◽  
Fourier Space ◽  
Ccd Cameras ◽  
Simulated Image ◽  
Initial Sampling ◽  
Fourier Algorithm

The conventional discrete Fourier transform can be extended to a discrete Extended Fourier transform (EFT). The EFT allows to work with discrete data in close analogy to the optical bench, where continuous data are processed. The EFT includes a capability to increase or decrease the resolution in Fourier space (thus the argument that CCD cameras with a higher number of pixels to increase the resolution in Fourier space is no longer valid). Fourier transforms may also be shifted with arbitrary increments, which is important in electron holography. Still, the analogy between the optical bench and discrete optics on a computer is limited by the Nyquist limit. In this abstract we discuss the capability with the EFT to change the initial sampling rate si of a recorded or simulated image to any other(final) sampling rate sf.

scholarly journals Higher Rank Wavelets

2011 ◽  
Vol 63 (3) ◽  
pp. 689-720
Author(s):  
Sean Olphert ◽  
Stephen C. Power
Keyword(s):  
Orthonormal Basis ◽  
Fourier Transforms ◽  
Latin Square ◽  
Haar Wavelets ◽  
Scaling Functions ◽  
Wavelet Sets ◽  
Compactly Supported ◽  
Rank 2 ◽  
Higher Rank ◽  
Meyer Wavelet

Abstract A theory of higher rank multiresolution analysis is given in the setting of abelian multiscalings. This theory enables the construction, from a higher rank MRA, of finite wavelet sets whose multidilations have translates forming an orthonormal basis in L2(ℝd). While tensor products of uniscaled MRAs provide simple examples we construct many nonseparable higher rank wavelets. In particular we construct Latin square wavelets as rank 2 variants of Haar wavelets. Also we construct nonseparable scaling functions for rank 2 variants of Meyer wavelet scaling functions, and we construct the associated nonseparable wavelets with compactly supported Fourier transforms. On the other hand we show that compactly supported scaling functions for biscaled MRAs are necessarily separable.

A Numerical Scheme for Generalized Peierls-Nabarro Model of Dislocations Based on the Fast Multipole Method and Iterative Grid Redistribution

2015 ◽  
Vol 18 (5) ◽  
pp. 1282-1312 ◽  
Author(s):  
Aiyu Zhu ◽  
Congming Jin ◽  
Degang Zhao ◽  
Yang Xiang ◽  
Jingfang Huang
Keyword(s):  
Boundary Conditions ◽  
Long Range ◽  
Numerical Scheme ◽  
Fast Multipole Method ◽  
Dislocation Core ◽  
Elastic Interaction ◽  
Epitaxial Thin Films ◽  
Fast Multipole ◽  
Multipole Method ◽  
Grid Points

AbstractDislocations are line defects in crystalline materials. The Peierls-Nabarro models are hybrid models that incorporate atomic structure of dislocation core into continuum framework. In this paper, we present a numerical method for a generalized Peierls-Nabarro model for curved dislocations, based on the fast multipole method and the iterative grid redistribution. The fast multipole method enables the calculation of the long-range elastic interaction within operations that scale linearly with the total number of grid points. The iterative grid redistribution places more mesh nodes in the regions around the dislocations than in the rest of the domain, thus increases the accuracy and efficiency. This numerical scheme improves the available numerical methods in the literature in which the long-range elastic interactions are calculated directly from summations in the physical domains; and is more flexible to handle problems with general boundary conditions compared with the previous FFT based method which applies only under periodic boundary conditions. Numerical examples using this method on the core structures of dislocations in Al and Cu and in epitaxial thin films are presented.

Chebyshev Wavelet Quasilinearization Scheme for Coupled Nonlinear Sine-Gordon Equations

2016 ◽  
Vol 12 (1) ◽  
Author(s):  
K. Harish Kumar ◽  
V. Antony Vijesh
Keyword(s):  
Basis Function ◽  
Numerical Scheme ◽  
Function Method ◽  
Gordon Equation ◽  
Basic Function ◽  
Sine Gordon Equation ◽  
One Dimensional ◽  
Improve Accuracy ◽  
Chebyshev Wavelet ◽  
Grid Points

Radial basis function (RBF) has been found useful for solving coupled sine-Gordon equation with initial and boundary conditions. Though this approach produces moderate accuracy in a larger domain, it requires more grid points. In the present study, we develop an alternative numerical scheme for solving one-dimensional coupled sine-Gordon equation to improve accuracy and to reduce grid points. To achieve these objectives, we make use of a wavelet scheme and solve coupled sine-Gordon equation. Based on the numerical results from the wavelet-based scheme, we conclude that our proposed method is more efficient than the radial basic function method in terms of accuracy.

scholarly journals Laguerre semigroup and Dunkl operators

2012 ◽  
Vol 148 (4) ◽  
pp. 1265-1336 ◽  
Author(s):  
Salem Ben Saïd ◽  
Toshiyuki Kobayashi ◽  
Bent Ørsted
Keyword(s):  
Unitary Representation ◽  
Fourier Transforms ◽  
Universal Covering ◽  
Hankel Transform ◽  
Kernel Functions ◽  
Difference Operators ◽  
Dunkl Transform ◽  
Dunkl Operators ◽  
Hermite Semigroup ◽  
Heisenberg Uncertainty

AbstractWe construct a two-parameter family of actionsωk,aof the Lie algebra 𝔰𝔩(2,ℝ) by differential–difference operators on ℝN∖{0}. Herekis a multiplicity function for the Dunkl operators, anda>0 arises from the interpolation of the two 𝔰𝔩(2,ℝ) actions on the Weil representation ofMp(N,ℝ) and the minimal unitary representation of O(N+1,2). We prove that this actionωk,alifts to a unitary representation of the universal covering ofSL(2,ℝ) , and can even be extended to a holomorphic semigroup Ωk,a. In thek≡0 case, our semigroup generalizes the Hermite semigroup studied by R. Howe (a=2) and the Laguerre semigroup studied by the second author with G. Mano (a=1) . One boundary value of our semigroup Ωk,aprovides us with (k,a) -generalized Fourier transforms ℱk,a, which include the Dunkl transform 𝒟k(a=2) and a new unitary operator ℋk (a=1) , namely a Dunkl–Hankel transform. We establish the inversion formula, a generalization of the Plancherel theorem, the Hecke identity, the Bochner identity, and a Heisenberg uncertainty relation for ℱk,a. We also find kernel functions for Ωk,aand ℱk,afora=1,2 in terms of Bessel functions and the Dunkl intertwining operator.

scholarly journals Fourier transforms of powers of well-behaved 2D real analytic functions

2018 ◽  
Vol 30 (3) ◽  
pp. 723-732
Author(s):  
Michael Greenblatt
Keyword(s):  
Analytic Functions ◽  
Fourier Transforms ◽  
Newton Polygon ◽  
Companion Paper ◽  
Two Dimensional ◽  
Compactly Supported ◽  
Sharp Estimates ◽  
Real Analytic Functions ◽  
Real Analytic ◽  
Compactly Supported Functions

AbstractThis paper is a companion paper to [6], where sharp estimates are proven for Fourier transforms of compactly supported functions built out of two-dimensional real-analytic functions. The theorems of [6] are stated in a rather general form. In this paper, we expand on the results of [6] and show that there is a class of “well-behaved” functions that contains a number of relevant examples for which such estimates can be explicitly described in terms of the Newton polygon of the function. We will further see that for a subclass of these functions, one can prove noticeably more precise estimates, again in an explicitly describable way.

scholarly journals Interactive Tools for Teaching Fourier Transforms

2020 ◽  
Vol 1 (1) ◽  
pp. 4
Author(s):  
Carlos R. Baiz
Keyword(s):  
Fourier Transforms ◽  
Lesson Plan ◽  
Real Space ◽  
Fourier Space ◽  
Core Component ◽  
Interactive Approach ◽  
Interactive Teaching ◽  
Mathematical Skills ◽  
Interactive Tools ◽  
Upper Level

Fourier transforms (FT) are universal in chemistry, physics, and biology. Despite FTs being a core component of multiple experimental techniques, undergraduate courses typically approach FTs from a mathematical perspective, leaving students with a lack of intuition on how an FT works. Here, I introduce interactive teaching tools for upper-level undergraduate courses and describe a practical lesson plan for FTs. The materials include a computer program to capture video from a webcam and display the original images side-by-side with the corresponding plot in the Fourier domain. Several patterns are included to be printed on paper and held up to the webcam as input. During the lesson, students are asked to predict the features observed in the FT and then place the patterns in front of the webcam to test their predictions. This interactive approach enables students with limited mathematical skills to achieve a certain level of intuition for how FTs translate patterns from real space into the corresponding Fourier space.

scholarly journals Randomized Benchmarking as Convolution: Fourier Analysis of Gate Dependent Errors

Quantum ◽  
2021 ◽  
Vol 5 ◽  
pp. 581
Author(s):  
Seth T. Merkel ◽  
Emily J. Pritchett ◽  
Bryan H. Fong
Keyword(s):  
Fourier Analysis ◽  
Recent Work ◽  
Fourier Transforms ◽  
Decay Rates ◽  
Alternative Proof ◽  
Mathematical Framework ◽  
Fourier Space ◽  
Clifford Group ◽  
Depolarizing Channel ◽  
The Ideal

We show that the Randomized Benchmarking (RB) protocol is a convolution amenable to Fourier space analysis. By adopting the mathematical framework of Fourier transforms of matrix-valued functions on groups established in recent work from Gowers and Hatami \cite{GH15}, we provide an alternative proof of Wallman's \cite{Wallman2018} and Proctor's \cite{Proctor17} bounds on the effect of gate-dependent noise on randomized benchmarking. We show explicitly that as long as our faulty gate-set is close to the targeted representation of the Clifford group, an RB sequence is described by the exponential decay of a process that has exactly two eigenvalues close to one and the rest close to zero. This framework also allows us to construct a gauge in which the average gate-set error is a depolarizing channel parameterized by the RB decay rates, as well as a gauge which maximizes the fidelity with respect to the ideal gate-set.

Memory-efficient source wavefield reconstruction and its application to 3D reverse time migration

Geophysics ◽  
2021 ◽  
pp. 1-76
Author(s):  
Zhiming Ren ◽  
Qianzong Bao ◽  
Shigang Xu
Keyword(s):  
Conventional Method ◽  
Reconstruction Method ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Time Step ◽  
Time Migration ◽  
Spatial Grid ◽  
Grid Points ◽  
Backward Propagation ◽  
And Storage

Reverse time migration (RTM) generally uses the zero-lag crosscorrelation imaging condition, requiring the source and receiver wavefields to be known at the same time step. However, the receiver wavefield is calculated in time-reversed order, opposite to the order of the forward-propagated source wavefield. The inconvenience can be resolved by storing the source wavefield on a computer memory/disk or by reconstructing the source wavefield on the fly for multiplication with the receiver wavefield. The storage requirements for the former approach can be very large. Hence, we have followed the latter route and developed an efficient source wavefield reconstruction method. During forward propagation, the boundary wavefields at N layers of the spatial grid points and a linear combination of wavefields at M − N layers of the spatial grid points are stored. During backward propagation, it reconstructs the source wavefield using the saved wavefields based on a new finite-difference stencil ( M is the operator length parameter, and 0 ≤  N ≤  M). Unlike existing methods, our method allows a trade-off between accuracy and storage by adjusting N. A maximum-norm-based objective function is constructed to optimize the reconstruction coefficients based on the minimax approximation using the Remez exchange algorithm. Dispersion and stability analyses reveal that our method is more accurate and marginally less stable than the method that requires storage of a combination of boundary wavefields. Our method has been applied to 3D RTM on synthetic and field data. Numerical examples indicate that our method with N = 1 can produce images that are close to those obtained using a conventional method of storing M layers of boundary wavefields. The memory usage of our method is ( N + 1)/ M times that of the conventional method.

scholarly journals Three-dimensional marginal separation

1989 ◽  
Vol 202 ◽  
pp. 559-575 ◽  
Author(s):  
P. W. Duck
Keyword(s):  
Boundary Layer ◽  
Integral Equation ◽  
Numerical Scheme ◽  
Nonlinear Integral Equation ◽  
Three Dimensional ◽  
Physical Space ◽  
Displacement Function ◽  
Two Dimensional ◽  
Fourier Space ◽  
Key Equation

The three-dimensional marginal separation of a boundary layer along a line of symmetry is considered. The key equation governing the displacement function is derived, and found to be a nonlinear integral equation in two space variables. This is solved iteratively using a pseudospectral approach, based partly in double Fourier space, and partly in physical space. Qualitatively the results are similar to previously reported two-dimensional results (which are also computed to test the accuracy of the numerical scheme); however quantitatively the three-dimensional results are much different.

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